Electrical adjustment of time-constant apparatus

ABSTRACT

An auxiliary circuit for adjusting the time-constant of electrical apparatus, such as that of a relaxation oscillator having resistor-capacitor time-constant circuit elements. The adjustment is maintained while an electrical adjusting signal is present. This biases a transistor into conduction and places a second resistor in parallel with the basic resistor of the timeconstant circuit, thereby reducing the time-constant. Alternate embodiments selectively allow plural adjustments, also adjustment of plural separate electrical devices.

United States Patent [15] 3,660,690 Theodore [4 1 May 2, 1972 54]ELECTRICAL ADJUSTMENT OF TIME- 3,260,864 7/1966 Nourney ..307/273 xCONSTANT APPARATUS 3,278,684 l0/l966 Geraghty et al ..307/273 X3,346,746 10/1967 Gordon ..307/273 [72] Inventor: Charles Theodore,Huntington Beach,

Cahf- Primary Examiner-Donald D. Forrer 73 Assignee: LTV Ling Altec,lnc., Anaheim, Calif. wwdbmge Attorney-Harry R. Lubcke [22] Filed: Nov.9, 1970 [21] Appl. No.: 87,689 [57] ABSTRACT An auxiliary circuit foradjusting the time-constant of electri- 52] U 5 Cl 307/293 307/265 331/]13 cal apparatus, such as that of a relaxation oscillator having re-[511 03k 3/10 sister-capacitor time-constant circuit elements. Theadjust- [58] Fieid 331/ 13 ment is maintained while an electricaladjusting signal is v present. This biases a transistor intoconductionand places a second resistor in parallel with thebasic-resistor of the time- [56] References Cited constant circuit,thereby reducing the time-constant. Al-

UNITED STATES PATENTS temate embodiments selectively allow pluraladjustments, also 3 258 605 6/1966 C] k 307/273 X adjustment of pluralseparate electrical devices. a

ar 3,227,891 l/ l 966 Asheraft 2 Claims, 4 Drawing Figures COMMAND "3|COMMAND FIG. 2.

COMMAND -3| CHARLES mzooons B IQM AGENT INVENTOR COMMAND zo'ff FIG. 1.

FIG. 3.

FIG. 4.

ELECTRICAL ADJUSTMENTOF TIME-CONSTANT APPARATUS BACKGROUND OF THEINVENTION This invention pertains to the alteration of an electricalcharacteristic of a device that occurs in the presence of an electricalsignal'in an auxiliary circuit.

The prior art has altered the period of time-constant circuits byphysically connecting additional circuit elements to the basictime-constant circuit-This has been accomplished by manual switching,relay switching, or by means of a motordriven switch.

The prior art has also altered the voltage to which a timeconstantresistor is returned, thereby altering the time required to charge theassociated capacitorto the voltage at which relaxation takes place inan'oscillator of the relaxation type. However, this requires that thealtered voltage be regulated so that the relaxation period is stable andrepeatable.

SUMMARY OF THE INVENTION In essence, a non-critical amplitude ofelectrical energy determines that an additional element shall either beincluded or excluded from functioning coactively with a similar type ofelement that is permanently connected in circuit.

Typically, a second resistor is placed in parallel with the resistor ofa resistor capacitor time-constantcircuit by current flow through asemiconductor device that is auxiliary to the main circuit. More thanone resistive element maybe placed parallel by including additionalsemiconductor devices, .which may be selectively caused to conduct.Also, one control circuit can be arranged to add an additionaltime-constantele ment to each of plural separate electrical devices. Aunilateral conductor is included in series with each additional time-conBRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of atime-constant circuit apparatus to which an additional resistive elementis added b the presence of a signal in an auxiliary circuit.

FIG. 2 is the same for selectively adding either or both of twoadditional resistive elements. 7

FIG. 3 is a schematic diagram for individually adding resistive elementsto each of two time-constant circuits while retaining isolation of thesecircuits.

FIG. 4 is the schematic diagram for one monostable mul tivibrator, whichis typical of those shown in block form in the other figures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 block 20 indicates atypical circuit, the time-constant of which is reduced during thepresence of an auxiliary signal from command entity 21. The internalconnections of the circuit of block 20 are given in FIG. 4, keyed to thereference numerals within the block. FIG. 4 shows a monostablemultivibrator as illustrative. Other relaxation oscillators and devicesof similar nature may be substituted for the circuit to be electricallyadjusted according to this invention.

The first resistive element is resistor 22 in FIG. 1. Capacitor 23, inseries therewith, is the second component of the timeconstant circuit.In FIG. 1 these elements determine the period of relaxation of themonostable multivibrator detailed in FIG. 4. The capacitor connects tointernal connection 4, the resistor to 3 and also to 16, which in turnis connected to terminal 24. This terminal represents a source ofpositive voltage supply (not shown) the negative terminal of which isconnected to ground. A voltage of 12 volts is typical for this source.

bias upon the base of 3 volts. At normal bias transistor 26 isnon-conductive, at a bias three volts less 'it is fully conductive.Typical values for resistors 22 and 25 are in the thousands of ohms, asin the range of from 10,000 to 50,000 ohms. Thus. the small internalresistance of transistor 26 when it is conducting is negligible. Atypical value for. capacitor 23 may be in the range of from a smallfraction of -a microfarad to less than one-thousandth of a microfarad.

The exact circuit and mode of operation of command entity 21 is notsignificant with respect to the present invention. It is. merely to givean alteration of bias to the base of transistor 26 to cause thetransistor to conduct when a reduced time constant is desired, and viceversa. The return circuit is to ground, which is common throughout thecircuit as a whole. In its highest usefulness the output from thecommand entity occurs because of an alteration in the mode of operationof circuits associated with the circuit of FIG. 1. Such alterationrequires a change in the time-constant of the circuit of FIG. I, as toincrease the frequency of oscillation of a relaxation oscillator for adecrease in theperiod of the time constant, to increase the rapidity ofactuation of a monostable 'multivibrator (reduce the delay time), or tosimilarly alter the function of any circuit involved with atime-constant circuit for block 20. Such a system is fully automatic anddoes not need manual alteration of the time-constant, which might beimpossible in unattended apparatus.

FIG. 2 follows the technology of FIG. 1 except that provision for addingeither or both of twoadditional resistors to decrease the time-constantof the resistor-capacitor circuit has been made. This makes availablefour different time-constant values. The short dotted line aligned withthe transistors in FIG. 2 indicates that by the structure set forth inthat FIG. 2 a

third transistor and resistor may be added, a fourth, etc., etc.,

30', the second terminal thereof being connected to internal connection3. The emitter of transistor 29 is connected to positive terminal 24 asbefore. Internal connection 16, also connected to terminal 24, completesthe circuit of each of the series configurations of resistor andtransistor so that the timeconstant circuit will be effective in theinternal circuit of device 20.

FIG. 3 is the schematic diagram for accomplishing something quitedifferent from the accomplishment of FIG. 2; the control of twotime-constants in separate circuits by one control means while retainingisolation of the circuits. The invention is merely applied in adifferent manner.

Two circuits, 20 and 20 are now involved. For simplicity these have beentaken as substantially the same, and in accordance with FIG. 4 herein.It is not necessary that this be so; only that each be suited to controlby an external time-constant circuit. For block circuit 20 these are 23and 22, as before, with 25 the resistor that is added. For block circuit20' these are similar, but bear the numerals 32, 33 and 34,respectively.

As practiced, the delay provided by circuit 20' was about oneone-hundredth that of circuit 20. For circuit 20 resistor 22 had a valueof 56,000 ohms, resistor 25 a value of 8,200 ohms, and capacitor 23 avalue of 0.039 microfaradFor circuit 20' resistor 32 had a value of56,000 ohms, resistor 34 a value of 27,000 ohms, and capacitor 33 avalue of 390 picofarads.

sistor 37 had a resistance of 8,200 ohms and resistor 38 of 10,000 ohms.Resistor 39, of 10,000 ohms is in series from the common connectionbetween resistors 37 and 38 and the base of transistor 36. It acts inconjunction with diode 40, con nected from the base to terminal 24, withthe anode of the diode connected to the base of the transistor. Thefunction of the diode is to limit the reverse base-emitter voltage ofthe transistor to 0.6 volt.

A- first unilateral conductor, diode 41 in FIG. 3, is connected withcathode to second resistive element 25. A second unilateral conductor,diode 42, is similarly connected to additional resistive element 34. Theanodes of each of these are connected together and to the collector oftransistor 36. A further resistor 43 connects from that collector to asource of negative voltage, indicatedby terminal .44. A voltage of minus12 volts is suitable-and the positive terminal of the power supply,(notshown) ,is'connected to .ground. A resistance of 100,000 ohms forresistor 43 is suitable. Capacitor 45 is connected from the anodes ofthe diodes to ground, has a capacitance of 0.1 microfarad, and ispresent for the purpose of reducing noise in the circuit; i.e., unwantedfluctuations of relatively high frequency.

The above circuit is proportioned so that diodes 41 and 42 areback-biased (i.e., non-conductive) when resistors 25 and 34 are not tobe included in the time-constant circuits. This is accomplished by thenegative voltage source 44. However, when transistor v36 is renderedconductive by a command signal on itsbase the resulting equivalentconnection to positive voltage source 24 overcomes the negativepotential from negative source 44 anda positive voltage exists at theanodes of both diodes 41- and 42. This reduces the impedance of thediodes from substantially an open circuit to a very low value inrelation to the resistance of the resistors and these are therefore incircuit. As soon as the command signal leaves the situation is reversedto its initial state.

In addition to the circuit postulated for the command blocks 21;, '21and 31 thus far it will be realized that these may be actuated fromassociated equipment by electrical energy in the form of pulses. In thisinstance the command'circuits include latching 'circuits,'which place agiven bias on the output upon receiving one pulse and remove it uponreceiving a second pulse. Depending upon the natureof the pulsesavailable and the nature of the latching circuit employed the secondpulse may be of reverse polarity to the polarity of the first pulse, orit may not be.

Diodes 41 and 42 may each be of the 1N4l48 type. FIG. 4 gives theschematic diagram for an illustrative circuit for the 20 and 20' blocksin the previous figures. This is a -one-shot" or monostablemultivibrator, an integrated circuit manufactured by AmelcoSemiconductor (Co.). Since this is a commercially obtainable product,being Type 342, only the significant aspects of thecircuit will bedescribed, particularly with reference 'to the previously mentionedinternal connections shown within the blocks. These are the externalconnections when considered from the viewpoint of the circuit within theblock.

n In FIG. 4 N PN transistors 50 and 51 are the basic transistors I ofthe monostable multivibrator. In the cross connection between the two,terminals 3 and 4 are interposed. It is here that this part of theinternal circuit is completed by capacitor 23 of this invention.Similarly, resistor 22 is connected between terminals 3 and 16. Both ofthese external elements are shown dotted in FIG. 4 for completeness.,The five other transistors shown arefor purposes of isolation andamplification. That is, transistor circuit 50,51 is isolated fromvarious impedance values of both loads and input circuits by thesetransistor circuits. In this way the basic circuit performs consistentlyas to timing and other aspects regardless of external impedances. Also,to provide reasonable power to drive subsequent circuits certain of thetransistors not only give impedance isolation but also give powerincrease.

External trigger connection 6 may be regarded as the input to themonostable multivibrator. It is here that a pulseis impressed prior tothe delay of the same that is soughtby the use of this circuit. Thistriggers the monostable multivibrator from one state to the other.

The output circuits are 2 and 5, also known as Q and G. The Q circuitgoes positive when the monostable multivibratorjs triggered and remainspositive for the duration of the timeconstant provided by thisinvention. The 6 circuit goes nega-.

tive for a similar period. These output circuits have been shown in theseveral figures herein, but use circuits connected to the same have notbeen shown since these may take many forms depending upon the purposeinvolved and are not pertinent to the invention. 7

Circuit connection 16 is supplied with positive voltage for operatingthe internal circuit by connection to source terminal tion withrespectto ground. Time-constant terminal. 12 is the' same as terminal 4and 13 is the same as-3. Output terminal 14 is the same as prior outputterminal 2, and terminal 11 is the same as 5. All of the outputterminals need not be used in any particular application. The internalfunctioning is not altered in such a circumstance. Terminals 16 and 8are carried through to circuit 20'. 7

Circuit 20, may, of course, be an encapsulated circuit or a circuitformed of separate components instead of having the integrated form. Itmay also be simplified or modified to other circuits requiring anexternal time-constant circuit with electrical control for the changingof the time-constant.

Hereinafter, the first means to connect the second resistive element inseries with the pair of current-carrying connections is the conductorbetween resistor 25 and the collector of transistor 26, while the secondmeans to connect comprise. the conductorsfrom the emitter of transistor26 to terminal 24 and from resistor 25 to the connection of resistor 22to terminal 3.

I claim: 1. Electrical means for reducing the time-constant for anelectrical circuit (20), comprising;

a. a first resistive element (22) connected to said electrical circuitand determining in part said time constant, b. a second resistiveelement (25),

c. a semiconductor device (26) having a pair of current-carryingconnections and a control connection, d. first means to connect saidsecond resistive element in series with said pair of current-carryingconnections,

e. second means to connect the series circuit of said second resistiveelement and said pair of current-carrying conh. a second electricalcircuit (20') having an inherent resistive element (32), t

i. an additional resistive element (34),

j. a second unilateral conductor (42), and

k. additional means to connect said additional resistive element (34),said second unilateral conductor, and said pair of current-carryingconnections in an additional 'series circuit and to said secondelectrical circuit (20),

whereby said command means (31) connected to said control connection ofsaid semiconductor device (36) to selectively produce conduction betweensaid pair of current-carrying connections separately connects saidsecond resistive element (25) in parallel with said first resistiveelement (22) and also said additional resistive element (34) in parallelwith said inherent resistive element (32).

Y 2. The means of claim 1 which additionally includes;

* I I l

1. Electrical means for reducing the time-constant for an electricalcircuit (20), comprising; a. a first resistive element (22) connected tosaid electrical circuit and determining in part said time constant, b. asecond resistive element (25), c. a semiconductor device (26) having apair of current-carrying connections and a control connection, d. firstmeans to connect said second resistive element in series with said pairof current-carrying connections, e. second means to connect the seriescircuit of said second resistive element and said pair ofcurrent-carrying connections in shunt to said first resistive element,f. command means (21) connected to said control connection toselectively produce conduction between said pair of currentcarryingconnections, g. a first unilateral conductor (41) interposed in saidseries circuit of said second resistive element (25) and said pair ofcurrent-carrying connections, h. a second electrical circuit (20'')having an inherent resistive element (32), i. an additional resistiveelement (34), j. a second unilateral conductor (42), and k. additionalmeans to connect said additional resistive element (34), said secondunilateral conductor, and said pair of current-carrying connections inan additional series circuit and to said second electrical circuit(20''), whereby said command means (31) connected to said controlconnection of said semiconductor device (36) to selectively produceconduction between said pair of current-carrying connections separatelyconnects said second resistive element (25) in parallel with said firstresistive element (22) and also said additional resistive element (34)in parallel with said inherent resistive element (32).
 2. The means ofclaim 1 which additionally includes; a. a bias source (44), b. a seriesimpedance (43), and c. means to connect said bias source through saidseries impedance to said first and second unilateral conductors to biasthese unilateral conductors into non-conduction save when conduction isproduced between the pair of current-carrying connections of saidsemiconductor device (36).